KR20040039379A - Thermoconductive composition - Google Patents

Abstract

In the thermally conductive composition containing the wax, substantially spherical boron nitride is added as filler. The average particle size of the substantially spherical boron nitride is preferably 20 to 100 mu m, and the filling rate is preferably 10 to 30 vol%.

Description

Thermally Conductive Composition {THERMOCONDUCTIVE COMPOSITION}

In recent years, removing heat from heating elements has become an important problem in many fields. In particular, heat is removed from heat generating electronic components (for example, IC chips) or other components (hereinafter collectively referred to as "heat generating components") built in various devices such as, for example, electronic devices and personal computers. It is becoming an important issue. This is because, as the temperature of various heat generating parts rises, the probability of malfunction of the parts tends to increase exponentially. More recently, as heat generating parts have become smaller and processing speeds become higher, requirements for heat generating parts have become more stringent.

At present, in order to release the heat accumulated and generated from the heat generating parts, for example, heat sinks such as heat sinks, heat radiation fins, and metal heat sinks are mounted on the heat generating parts. In addition, various thermally conductive materials or sheets are used as heat transfer spacers between the heat generating parts and the heat sinks in order to act as the thermally conductive material or sheet.

For example, greases containing thermally conductive fillers have extremely low thermal resistance and have been commonly used as thermally conductive materials. The grease itself exhibits excellent thermal conductivity, but since the grease is a liquid, it takes a long time and requires a lot of effort when it is placed between the heating element and the heat sink. Therefore, grease has not only poor handleability, but also has a problem of difficulty in surrounding contamination or coating of a certain amount.

In order to solve this problem, a thermally conductive sheet obtained by forming a thermally conductive material in the form of a sheet has been proposed. High thermal conductivity fillers are highly charged to increase the thermal conductivity of conventional thermally conductive sheets. For example, European Patent Publication No. 0322165 or Japanese Patent Application Publication No. 11-26661 describes a thermally conductive sheet filled with boron nitride having a large particle size at a high filling rate of 30 to 60% by volume as a filler. However, these sheets are highly filled with fillers and the binder is a thermosetting resin or elastomer, so there is a problem that the compressive repulsion force is great when incorporated into the device. In addition, the sheet cannot be made to have an initial thickness of 300 to 500 µm or less due to the limitation of mechanical strength, and the thickness of the sheet incorporated into the apparatus also cannot be set to 200 to 300 µm or less because of its large compression repulsion force. Therefore, the thermal resistance of this sheet is extremely large compared to grease that can reduce the thickness after merging to several tens of micrometers.

On the other hand, the phase change type thermally conductive sheet using wax as a binder has high heat dissipation performance because the thickness of the sheet decreases after the melting of the wax and the phase change during heating causes the final thermal resistance to be similar to that of the grease. It is a thermally conductive sheet excellent in handleability. For example, JP 2000-509209 A describes a thermally conductive sheet containing plate-like boron nitride and wax having an average particle size of 7 to 10 μm. In this thermally conductive sheet, since the filler is plate-like and the binder is fluid, the sheet thickness after the phase change is reduced to 50 to 100 mu m, and the final thermal resistance is lowered similarly to the thermal resistance of grease. However, the plate-like boron nitride has anisotropy that the thermal conductivity in the plane direction is about 20 times or more than the thermal conductivity in the thickness direction, and when the plate-like boron nitride is formed into a sheet, since the plate crystal is oriented in the plane direction of the sheet, The thermal conductivity in the thickness direction is low and the initial thermal resistance before the phase change is extremely high. As a result, the start-up program is started due to excessive overheating of the heat generating parts merged into the sheet during the initial power charging to check the starting of the device, causing a loss of time to wait for the parts to cool down.

Problems to be Solved by the Invention

The present invention aims to solve the above problems and, in particular, to provide a thermally conductive composition capable of reducing initial thermal resistance upon device startup.

Means for solving the problem

According to the invention, this object can be achieved by a thermally conductive composition comprising a wax and substantially spherical boron nitride. By incorporating substantially spherical boron nitride as the thermally conductive filler, the thermally conductive sheet can have a significantly higher thermal conductivity in the thickness direction of the sheet than the thermal conductivity when using plate-like boron nitride particles, and reduce the initial thermal resistance before the phase change. .

The present invention relates to a thermally conductive composition, and more particularly, to a thermally conductive composition useful for dissipating heat to the outside by being in close contact with a heat generating electronic component such as a CPU.

The thermally conductive composition of the present invention contains wax and substantially spherical boron nitride as essential components. The wax is not particularly limited, and natural waxes, synthetic waxes or mixed waxes can be used. Examples of natural waxes include vegetable waxes such as candelilla wax, carnauba wax, rice wax, wax and jojoba oil; Animal waxes such as beeswax, lanolin and sperm; Mineral waxes such as montan wax, wax and ceresin; Petroleum waxes such as paraffin wax, microcrystalline wax and petrolactam. Examples of synthetic waxes include synthetic hydrocarbons such as Fischer-Tropsch wax and polyethylene wax; Modified waxes such as montan wax derivatives, paraffin wax derivatives and microcrystalline wax derivatives; Hydrogenated waxes such as hydrogenated castor oil and derivatives of hydrogenated castor oil; Fatty acids, acid amides, esters, ketones, and other waxes such as 12-hydroxy stearic acid, stearic acid amide, phthalic anhydride and chlorinated hydrocarbons. Melting | fusing point of this wax becomes like this. Preferably it is 30 degreeC-150 degreeC, More preferably, it is 40 degreeC-80 degreeC.

Substantially spherical boron nitride can be obtained, for example, by granulating the primary crystals of boron nitride using a spraying method or the like to sinter the obtained particles or to prepare a sinter-molded block and to crush the block. The boron nitride used in the present invention is substantially spherical, includes particles having an aspect ratio of 1 to 5, and further includes elliptical particles. When boron nitride is plate-shaped and the sheet formed of the thermally conductive composition containing boron nitride is disposed between the heat-generating component and the heat sink as described above, the boron nitride is oriented in the plane direction of the sheet, so that in the thickness direction of the sheet It is not possible to exert sufficiently high thermal conductivity. On the other hand, when the boron nitride is spherical, the thermal conductivity in the thickness direction of the sheet can increase, and in particular, the initial thermal resistance before the phase change can be reduced.

The average particle size of such substantially spherical boron nitride is preferably 20 to 100 m, more preferably 30 to 60 m. When the average particle size of the boron nitride particles used is less than 20 μm, the thermal conductivity in the thickness direction is lowered. When the average particle size of the particles is more than 100 μm, the thickness of the thermally conductive sheet after the phase change can hardly be reduced, and sometimes the final heat Resistance increases. The filling rate of the substantially spherical boron nitride is preferably 10 to 30% by volume based on the total thermally conductive composition. When the filling rate is less than 10% by volume, a sufficiently high thermal conductivity can hardly be obtained. On the contrary, when the filling rate is higher than 30% by volume, the thickness of the thermally conductive sheet after the phase change can hardly be reduced, and sometimes the final thermal resistance is high.

The heat conductive composition of this invention can contain the compound represented by following formula (I) other than said wax and substantially spherical boron nitride.

In said formula, R <^1> and R <^2> is a C1-C3 alkyl group each independently, n shows the value of 100-100,000. In the compound represented by the formula (I), R ¹ and R ² are preferably both methyl groups. That is, the compound represented by the formula (I) is preferably polyisobutylene. The number n of repeating units is 100 to 100,000 and the molecular weight is preferably 1,000 to 1,000,000, more preferably 30,000 to 60,000. The compounding amount of the compound represented by the formula (I) is 10 to 1,000 parts by weight, preferably 20 to 100 parts by weight, per 100 parts by weight of the wax.

Compounds of formula I are liquid polymers having a pour point above room temperature (as defined by JIS K 2269). The thermally conductive composition containing the compound represented by the formula (I) does not contain an elastic component, has excellent fluidity upon dissolution, exhibits excellent heat dissipation properties, does not cause excessive adhesion, and improves brittleness of the sheet, A sheet having strength is provided, and remarkably excellent handleability is ensured.

The thermally conductive composition of the present invention may further contain a softener in addition to the compound represented by the formula (I). By adding a softener, the fluidity of the thermally conductive composition can be increased, the adhesion between the heat generating component and the heat sink can be improved, and the thermal conductivity can be further increased. Examples of softeners that may be used include vegetable softeners, mineral softeners and synthetic plasticizers that are compatible with waxes. Examples of vegetable softeners that may be used include cottonseed oil, linseed oil and rapeseed oil. Examples of mineral softeners that may be used include paraffinic oils, naphthenic oils and aromatic oils. Examples of synthetic plasticizers that can be used include dioctyl phthalate, dibutyl phthalate, dioctyl adipate, isodecyl adipate, dioctyl sebacate and dibutyl sebacate. Among these, naphthenic oil and paraffinic oil are preferable. The blending amount of the softener is 1,000 parts by weight or less, preferably 10 parts by weight or less per 100 parts by weight of the wax.

In addition to the above components, various additives commonly used in polymer chemistry may be added to the thermally conductive composition of the present invention. For example, a tackifier, a plasticizer, etc. can be added in order to adjust the adhesiveness of the formed sheet, and a flame retardant and antioxidant can be added in order to raise heat resistance. Other examples of additives include modifiers, heat stabilizers and colorants. Moreover, said substantially spherical boron nitride can be pretreated with surface treating agents, such as a silane coupling agent.

The heat conductive composition of this invention can be manufactured by mixing a predetermined amount of said each component. The thermally conductive composition can be formed into a sheet or film by methods known in the art. For example, wax, substantially spherical boron nitride, a desired compound represented by the formula (I), a softener and the like are kneaded in a heat mixer, and the kneaded material is coated like a liner by hot melt coating to form a sheet. Alternatively, the components are diluted with a suitable solvent and mixed in a mixer, and then the mixture is coated on a liner by solvent casting to form a sheet.

The sheet may be formed in various thicknesses depending on the purpose of use or the site of application thereof, but is generally as thin as possible, preferably 0.02 to 2.0 mm, more preferably 0.1 to 0.5 mm. If the thickness is less than 0.02 mm, a sufficiently high adhesive strength cannot be obtained between the heat generating part and the heat sink, so that satisfactory heat dissipation characteristics cannot be obtained. Extrusion from the fixed area is increased, causing unnecessary adhesion to the surroundings.

The sheet thus formed can be used as it is as a heat transfer means. However, if desired, this sheet can be used in combination with a suitable substrate. Examples of suitable substrates include plastic films, wovens, nonwovens, and metal foils. Examples of the woven fabric and the nonwoven fabric include woven fabric and nonwoven fabric made of glass, polyester, polyolefin, nylon, carbon, ceramic, and the like, or fibers coated with the metal. The substrate may be located at the sheet surface layer or at an intermediate layer thereof.

Since this sheet is solid at room temperature, it can be inserted between the heat generating parts and the heat sink, and has excellent handleability compared to the case of using liquid grease. When the heat generating component is activated, the inserted sheet is softened by the heat of the heat generating component to cause a phase change, and fills the gap between the heat generating component and the heat sink. In addition, since the thickness of the space between the heat generating component and the heat sink becomes considerably thin, the thermal resistance value can be greatly reduced. Therefore, the softening point of the heat conductive composition which comprises this sheet becomes like this. Preferably it is 30 degreeC-150 degreeC, More preferably, it is 40 degreeC-100 degreeC. The softening point can be arbitrarily selected according to the type and amount of the constituents.

In addition, this sheet, which contains a predetermined amount of the compound represented by the formula (I), has superior sheet strength such as tensile strength and bending strength as compared to conventional sheets using wax, and can be used without problems such as tearing or cracking of the sheet during use. have.

Example 1

Substantially spherical boron nitride agglomerates (Mizushima Gokin Tetsu Co., Ltd.) of 85 parts by weight of a binder containing 75 parts by weight of a paraffin wax having a melting point of 54 ° C., 25 parts by weight of polyisobutylene having a molecular weight of 40,000, and an average particle size of 50 μm with a filler (Mizushima Gokin Tetsu ) 15% by volume was uniformly kneaded at 80 ° C., and then the kneaded product was inserted between the upper liner and the lower liner and calendered at 80 ° C. to obtain a thermally conductive sheet having a thickness of 0.25 mm.

Example 2

A thermally conductive sheet was produced in the same manner as in Example 1, except that a substantially spherical boron nitride agglomerate (PT620, manufactured by Advanced Ceramics) having an average particle size of 20 µm was used as the filler.

Example 3

A thermally conductive sheet was produced in the same manner as in Example 1, except that a substantially spherical boron nitride agglomerate (obtained by classifying PT670 manufactured by Advanced Ceramics Co., Ltd.) was used as a filler.

Example 4

A thermally conductive sheet was produced in the same manner as in Example 1, except that the filling rate of the filler was changed to 25% by volume.

Comparative Example 1

A thermally conductive sheet was produced in the same manner as in Example 1, except that a substantially spherical boron nitride agglomerate (PT670, manufactured by Advanced Ceramics Co., Ltd.) having an average particle size of 200 to 300 µm was used as the filler. The thickness of the obtained sheet was 0.35 mm.

Comparative Example 2

A thermally conductive sheet was produced in the same manner as in Example 1, except that plate-like boron nitride (HP-1, manufactured by Mizushima Kohden Co., Ltd.) having an average particle size of 10 µm was used as the filler.

Comparative Example 3

A thermally conductive sheet was produced in the same manner as in Example 1 except that a plate-like boron nitride (PT110, manufactured by Advanced Ceramics Co., Ltd.) having an average particle size of 45 µm was used as the filler.

Comparative Example 4

A thermally conductive sheet was produced in the same manner as in Example 1, except that a substantially spherical alumina (CBA40, manufactured by Showa Denko K.K.) having an average particle size of 40 µm was used as the filler.

Comparative Example 5

A thermally conductive sheet was produced in the same manner as in Example 1, except that the filling rate of the filler was changed to 5% by volume.

Comparative Example 6

A thermally conductive sheet was produced in the same manner as in Example 1, except that the filling rate of the filler was changed to 35% by volume.

Comparative Example 7

A thermally conductive sheet was produced in the same manner as in Comparative Example 2, except that the filling rate of the filler was changed to 25% by volume.

<Evaluation of Properties of Thermally Conductive Sheets>

The thermally conductive sheets prepared as described above were cut to a size of 10 mm x 11 mm and peeled from the liner, respectively, inserted between the heat generating resistor and the cooling aluminum plate, and 20 W of power was applied to the heat generating resistor. After 30 seconds and 30 minutes after the power application, the temperature (T1) of the heat generating resistor and the temperature (T2) of the aluminum plate were measured, and the thermal resistance value was calculated according to the following equation (1). The heat resistance after 30 seconds was called initial heat resistance, and the heat resistance after 30 minutes was called final heat resistance.

Thermal resistance (℃ ㎠ / W) = (T1-T2) (℃) × sample area (㎠) / power (W)

The results obtained are shown in Table 1 below. As a reference example, the thermal resistance was similarly measured using thermally conductive grease (SE4490CV, manufactured by Dow Corning Toray Silicone Co.) with a thermal conductivity of 1.6 W / mK instead of the thermally conductive sheet.

Initial heat resistance (℃ ㎠ / W) Final heat resistance (℃ ㎠ / W) Example 1 2.2 1.3 Example 2 2.4 1.3 Example 3 2.2 1.7 Example 4 2.0 1.5 Comparative Example 1 2.6 3.0 Comparative Example 2 3.2 1.7 Comparative Example 3 3.1 1.4 Comparative Example 4 3.5 3.2 Comparative Example 5 4.5 2.9 Comparative Example 6 2.1 2.9 Comparative Example 7 2.8 2.2 Reference Example 1.1 1.3

As will be apparent from the above results, the thermally conductive sheet formed by using the composition of the present invention can lower both the initial thermal resistance and the final thermal resistance, and in particular, the initial thermal resistance is remarkably compared with the case of using a plate-shaped filler. Can be reduced.

By using substantially spherical boron nitride as a filler of the thermally conductive composition, the thermal conductivity of the thermally conductive sheet formed from the composition can be increased, and in particular, the initial thermal resistance before the phase change can be significantly reduced.

Claims (9)

A thermally conductive composition comprising a wax and spherical boron nitride. The thermally conductive composition according to claim 1, wherein the spherical boron nitride is contained in an amount of 10 to 30% by volume based on the total composition. The thermally conductive composition according to claim 1 or 2, wherein the spherical boron nitride has an average particle size of 20 to 100 µm. The thermally conductive composition according to any one of claims 1 to 3, further comprising 10 to 1,000 parts by weight of the compound represented by the following formula (I) per 100 parts by weight of the wax. <Formula I> In said formula, R <^1> and R <^2> is a C1-C3 alkyl group each independently, n shows the value of 100-100,000. The thermally conductive composition according to claim 4, wherein the compound represented by the formula (I) is polyisobutylene. The thermally conductive composition according to any one of claims 1 to 5, which is formed in the form of a film or sheet. The thermally conductive composition according to claim 6, wherein the film or sheet has a thickness of 0.02 to 2.0 mm. The thermally conductive composition of claim 1 wherein the wax is selected from natural waxes, synthetic waxes, and mixtures thereof. The thermally conductive composition of claim 1 wherein the wax is paraffin wax.